South Korea's nuclear safety body on Friday authorized the restart of a reactor that went offline due to a technical glitch late last month.

The Nuclear Safety and Security Commission (NSSC) said close inspection of the 950,000-kW Hanbit No. 2 reactor revealed there was a problem with circuitry while technicians were testing an emergency system.

It said the problem was with the Automatic Seismic Trip System on the reactor that was set up as an additional layer of safety following the Fukushima Dai-ichi partial nuclear meltdown.

"It is because of a glitch that the reactor went offline," the safety watchdog said.

It said technicians should have taken precautions when conducting the test to check the trip system.

The safety commission added that despite the reactor coming offline, all cooling systems that are critical to guard against a serious accident operated according to design, and there was never a risk to the reactor itself.

"In light of the accident, orders were issued to prevent a reoccurrence of such problems down the line," the commission said.

The No. 2 reactor is part of the larger Hanbit Nuclear Power Plant located 350 kilometers southwest of Seoul. It started commercial operation in June 1987.

There are currently six heavy water reactors at the Hanbit plant, with the last going online in late 2002. (Yonhap)